Autofocus actuator

ABSTRACT

An autofocus actuator is provided by which it is possible to easily confirm that a holder and a yoke do not make contact with each other even when the space between the holder and the yoke is made as small as possible in order to improve shock resistance. The autofocus actuator includes light transmission holes for confirming a space between an inner peripheral surface of an inner cylindrical portion of the yoke and an outer peripheral surface of a cylindrical portion of the holder provided with a lens unit and being capable of adjusting its position in the optical axis direction by supplying electrical power to a coil secured to the holder. The light transmission holes are provided at predetermined positions of a flange portion of the holder and a stopper for attaching a leaf spring to the holder, respectively, so that light can pass therethrough.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to an autofocus actuator, and inparticular to an autofocus actuator which can be used in a compactelectronic device equipped with a camera such as a digital camera orportable telephone or the like.

2. Description of the Prior Art

In digital cameras and the like, an actuator which can move lenses inthe optical axis direction by the interaction between a magnetic fielddue to a permanent magnet and a magnetic field generated by electriccurrent flowing through a coil is used for the purpose of carrying outautofocus and zoom. Further, with the recent development of megapixelimage taking elements having a pixel number of one million pixels ormore, there has been a demand for an autofocus function even in camerasinstalled in portable telephones.

A well-known prior art autofocus actuator is disclosed in JapaneseLaid-Open Patent Application No. 2004-280031. As shown in FIG. 20, aprior art autofocus actuator 100 is equipped with a yoke 130 having aroughly U-shaped cross-section, a permanent magnet 140 attached to theouter wall inner surface 132 of the yoke 130, a holder 110 (carrier)provided with a lens assembly 105 at a center position, a coil 120mounted in the holder 110, a base 185 in which the yoke 130 is mounted,a frame 180 which supports the base 185, and two leaf springs 160U, 160Lwhich support the holder 110. The holder 110 is inserted into a throughhole formed by an inner cylindrical portion 131 of the yoke 130. The twoleaf springs 160U, 160L are the same and are arranged to sandwich theholder 110 from above and below. Further, the two leaf springs 160U,160L function as a feeder circuit of the coil 120. By balancing thecurrent value applied to the coil 120 and the restoring force of the twoleaf springs 160U, 160L, it is possible to control the amount ofmovement of the lens assembly 105 mounted to the holder 110.

As an example of the external dimensions of an autofocus actuatormounted in a portable telephone, the length is approximately 10 mm, thewidth is approximately 10 mm, and the thickness is approximately 5 mm.

In the prior art autofocus actuator 100 described above, if the holder110 and the inner cylindrical portion 131 of the yoke 130 make contactwith each other, there is the problem that it becomes impossible to movethe lenses with good precision.

Further, if the space between the holder 110 and the inner cylindricalportion 131 of the yoke 130 is made large so that the holder 110 and theinner cylindrical portion 131 of the yoke 130 do not make contact witheach other in order to solve this problem, there is also the problemthat the shock resistance of the autofocus actuator 100 is degraded.

For example, in the case where a portable telephone falls from a heightwhere it was being used, the space between the holder 110 and the innercylindrical portion 131 of the yoke 130 needs to be made about 0.1 mm inorder to ensure sufficient shock resistance.

SUMMARY OF THE INVENTION

In view of the problems described above, it is an object of the presentinvention to provide an autofocus actuator which can easily confirm thata holder and a yoke do not make contact with each other even when thespace between the holder and the yoke is made as small as possible inorder to improve shock resistance.

In order to achieve the above object, the present invention is directedto an autofocus actuator which comprises:

a holder including a cylindrical portion having one end to which a lensunit is attached and a flange portion provided on the outer periphery ofthe other end of the cylindrical portion;

a coil fixedly secured to the flange portion of the holder in such amanner as to surround the cylindrical portion of the holder;

a yoke including an inner cylindrical portion having an insertion boreinto which the cylindrical portion of the holder is inserted, an outercylindrical portion provided outside the inner cylindrical portion witha predetermined spacing left therebetween, and a connecting portion forintegrally interconnecting the ends of the inner cylindrical portion andthe outer cylindrical portion at opposite side from the flange portionof the holder, the yoke adapted to accommodate the coil within the spaceof a predetermined gap size between the inner cylindrical portion andthe outer cylindrical portion;

a plurality of permanent magnets disposed on a magnet mounting surfaceof the inner periphery of the outer cylindrical portion of the yoke in aspaced-apart confronting relationship with the coil;

a pair of leaf springs including an upper leaf spring and a lower leafspring provided on opposite end sides in an optical axis direction ofthe cylindrical portion of the holder, respectively, for supporting theholder displaceably in the optical axis direction with the holder beingpositioned in a radial direction thereof; and

a stopper attached to the one end of the cylindrical portion of theholder which protrudes from the inner cylindrical portion of the yokefor supporting the upper leaf spring between the holder and the stopperin a sandwich manner, wherein the holder in which the lens unit isincorporated being capable of adjusting its position in the optical axisdirection by supplying electrical power to the coil;

wherein the autofocus actuator further comprising light transmissionmeans for confirming the space between the inner peripheral surface ofthe inner cylindrical portion and the outer peripheral surface of thecylindrical portion of the holder, the light transmission means beingprovided at predetermined positions of the flange portion and thestopper, respectively, so that light can pass therethrough.

According to the autofocus actuator having the structure describedabove, if the autofocus actuator is assembled precisely as designed,light can pass through from the light transmission means of either ofthe flange portion or the stopper to the light transmission means of theother through the space between the inner peripheral surface of theinner cylindrical portion of the yoke and the outer peripheral surfaceof the cylindrical portion of the holder. Therefore, by checking as towhether or light can pass through the light transmission means of theflange portion and the stopper in a state that the autofocus actuator isassembled, it is possible to confirm easily as to whether the innercylindrical portion of the yoke makes contact with the cylindricalportion of the holder.

Further, in the present invention, it is preferred that the lighttransmission means includes through holes formed in the flange portionand the stopper, respectively, so that light can pass through thethrough holes.

According to this structure, since the light transmittance means isformed from the through holes, the light can pass therethrough withoutbeing shielded by something, and this makes it possible to improve theaccuracy of confirming contact between the yoke and the holder.

Further, in the above structure, it is preferred that the through holesare sealed with a light transmittance material.

According to this structure, it is possible not only to confirm contactbetween the yoke and the holder, but also to prevent dust, water and thelike from entering into the inside of the autofocus actuator from thelight transmission means.

Further, in the autofocus actuator according to the present invention,it is preferred the each of the light transmission means is formed intoa thin film-shaped portion integrally formed in the flange portion andthe stopper.

According to this structure, it is possible not only to, confirm contactbetween the yoke and the holder, but also to prevent dust, water and thelike from entering into the inside of the autofocus actuator from thelight transmission means. In addition, the holder and the stopper havingsuch thin film-shaped portions as the light transmission means can bemade easily by integral molding without increasing the number of stepsof the conventional manufacturing process.

Further, in the autofocus actuator according to the present invention,it is preferred that on the outer periphery of the cylindrical portion,at least one protrusion is formed so as to extend in the axial directionof the cylindrical portion,

and the protrusion and the inner surface of the inner cylindricalportion are disposed so that they can be seen from the lighttransmission means.

According to this structure, by seeing light passing near the tip of theprotrusion in a state that the autofocus actuator is assembled, it ispossible to confirm easily as to whether the inner cylindrical portionof the yoke makes contact with the cylindrical portion of the holder.

Further, in the autofocus actuator according to the present invention,it is preferred the light transmission means in the flange portion, thelight transmission means in the stopper and the at least one protrusionare provided at three locations, respectively, so at to have apredetermined spacing in the circumferential direction thereof.

According to this structure, it is possible to see the space between theinner peripheral surface of the inner cylindrical portion and the outerperipheral surface of the cylindrical portion at three positions at thevery least, and this makes it possible to improve the accuracy ofconfirming contact between the yoke and the holder.

Furthermore, in the autofocus actuator according to the presentinvention, it is also preferred that the light transmission means in theflange portion and the light transmission means in the stopper arepositioned so as to be opposed to each other in the optical axisdirection.

According to this structure, it is possible to see the space between theinner peripheral surface of the inner cylindrical portion and the outerperipheral surface of the cylindrical portion in the spaces between thelight transmission means of the flange portion and the lighttransmission means of the stopper, and this makes it possible to improvethe accuracy of confirming contact between the yoke and the holderfurther.

Moreover, in the autofocus actuator according to the present invention,it is also preferred that each of the light transmission means is formedinto a roughly elliptical shape of which major axis bends in thecircumferential direction of the flange portion and the stopper.

According to this structure, it is possible to efficiently widen thearea in which it is possible to confirm contact between the innerperipheral surface of the inner cylindrical portion and the outerperipheral surface of the cylindrical portion without lowering thestrength of the flange portion and the stopper.

The above and other objects and features of the invention will becomemore apparent from the following detailed description when the same isread in conjunction with the accompanying drawings that are presentedfor the purpose of illustration only.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the external appearance of anautofocus actuator proposed by the inventor of the present invention andused as a base of the present invention;

FIG. 2 is an exploded perspective view of the autofocus actuator shownin FIG. 1;

FIG. 3 is a schematic cross-sectional view of the autofocus actuatorshown in FIG. 1;

FIG. 4 is a perspective view illustrating a yoke of cylindricalconfiguration;

FIG. 5 is a cross-sectional view of the yoke illustrating the state ofmagnetic field in case that a permanent magnet alone is attached to theyoke;

FIG. 6 is a cross-sectional view of the yoke illustrating the state ofmagnetic field in case that the permanent magnet is attached to the yokein combination with a magnetic member;

FIG. 7 is a perspective view illustrating the magnetic member of annularring shape;

FIG. 8 is a top view illustrating a leaf spring;

FIG. 9 is a top view illustrating a sheet-like electrode;

FIG. 10 is a partial schematic cross-sectional view of the autofocusactuator, illustrating the lead portion of a coil connected to thesheet-like electrode;

FIG. 11 is an enlarged view illustrating the part indicated by “A” inFIG. 10;

FIG. 12 is a top view showing the positional relationship between theflange portion of the holder, the lead portion of the coil and thesheet-like electrode;

FIG. 13 is a top view of a stopper;

FIG. 14 is a top view showing the positional relationship between theopening portion of a cover and the stopper;

FIG. 15 is a perspective view of an autofocus actuator of a preferredembodiment according to the present invention;

FIG. 16 is a perspective view of a holder of a preferred embodimentaccording to the present invention;

FIG. 17 is another perspective view of the holder of the preferredembodiment according to the present invention;

FIG. 18 is a perspective view illustrating a stopper of a preferredembodiment according to the present invention;

FIG. 19 is an enlarged plan view of a light transmission hole of thepreferred embodiment according to the present invention; and

FIG. 20 is a cross-sectional view illustrating the prior art autofocusactuator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An autofocus actuator proposed by the present inventor and used as abase of the present invention will be first described in detail withreference to the drawings attached.

Referring to FIG. 1, there is shown perspective view showing theexternal appearance of the autofocus actuator. FIG. 2 is an explodedperspective view of the autofocus actuator shown in FIG. 1. FIG. 3 is aschematic cross-sectional view of the autofocus actuator shown in FIG.1.

As shown in FIGS. 1, 2 and 3, the autofocus actuator 1 is generallycomposed of: a holder 10 including a cylindrical portion 11 having oneend to which a lens assembly 5 is attached, and a flange portion 12provided along the perimeter of the other end of the cylindrical portion11; a coil 20 fixedly secured to the holder 10 in a spaced-apartrelationship with the outer periphery of the cylindrical portion 11; acylindrical yoke 30 including an inner cylindrical portion 31 having aninsertion bore 35 into which the cylindrical portion 11 of the holder 10is inserted, an outer cylindrical portion 32 provided outside of theinner cylindrical portion 31 with a predetermined spacing lefttherebetween, and a connecting portion 34 for integrally interconnectingthe ends of the inner cylindrical portion 31 and the outer cylindricalportion 32 at opposite side from the flange portion 12 of the holder 10,the yoke 30 adapted to accommodate the coil 20 within the space ofpredetermined gap size between the inner cylindrical portion 31 and theouter cylindrical portion 32; a plurality of permanent magnets 40disposed on the magnet mounting surface 33 of the inner periphery of theouter cylindrical portion 32 of the cylindrical yoke 30 in aspaced-apart confronting relationship with the coil 20; a magneticmember 50 disposed to interconnect the permanent magnets 40 in such acondition that the magnetic member 50 is kept in contact with theopposite surfaces of the permanent magnets 40 from the connectingportion 34 of the cylindrical yoke 30; a pair of leaf springs (gimbalsprings) 60 including an upper leaf spring 60U and a lower leaf spring60L provided on opposite end sides in an optical axis direction of thecylindrical portion 11 of the holder 10 for supporting the holder 10displaceably in the optical axis direction with the holder beingpositioned in a radial direction thereof; a stopper 70 attached to theholder 10 for sandwichedly support the upper leaf spring 60U between theholder 10 and the stopper 70; a cover 80 and a base 85 which are used asa pair of support frames, respectively, and provided outside of thestopper 70 and the lower leaf springs 60L along the optical axisdirection and adapted to sandwichedly support the leaf springs 60between the opposite end surfaces of the yoke 30 and the respective oneof the cover 80 and the base 85, both of the cover 80 and the base 85having opening portions 80 a, 85 a respectively formed at least on theparts that correspond to the lens assembly 5 attached to the holder 10;and a sheet-like electrode 90 provided between the lower leaf spring 60Land the base 85 for supplying electric power to the coil 20.

Hereinbelow, a description will be made with regard to the details ofeach of the components mentioned above. In this regard, it should beappreciated that the term “upper”, “top” or its equivalent in thesubject specification denotes the

direction depicted by an arrow in FIG. 2, while the term “lower”,“bottom” or its equivalent means the reverse direction.

The holder 10 is a molded component made of synthetic resin. The holder10 has a cylindrical portion 11 of cylindrical configuration having oneend (upper end) to which a lens assembly 5 is attached, and an annularflange portion 12 integrally formed along the perimeter of the other end(lower end) of the cylindrical portion 11. As illustrated in FIG. 3, theinside of the cylindrical portion 11 of the holder 10 is formed into ahollow space. Further, the inner periphery of the cylindrical portion 11is formed with a female thread portion that can be threadedly engagedwith a male thread portion provided on the outer periphery of the lensassembly 5. On the peripheral edge of the top surface of the flangeportion 12 (the surface to the side of the cylindrical portion 11),there is provided a step portion 12 a to which the coil 20 is bonded inpositioning with the holder 10, as clearly shown in FIG. 3. Furthermore,on the bottom surface of the flange portion 12, a ring-shaped protrusion(step portion) 15 is concentrically formed, which is used forpositioning the lower leaf spring 60L with respect to the holder 10.Three small bosses 13 are integrally formed with the protrusion 15 at anequal spacing in such a manner that they can extend in parallel with theoptical axis.

As described above, the coil 20 is fixedly secured to the step portion12 a on the upper surface of the flange portion 12 of the holder 10 in aspaced-apart relationship with the outer periphery of the cylindricalportion 11 of the holder 10. A coated copper wire is used as the coil20. This coil 20 is formed by the varying-number-of-winding methodwherein a ten times winding layer and a nine times winding layer of thecopper wire are alternately laminated one atop the other. The coil 20 isformed into an air core coil having the cross-section of annular shape.The coil 20 is wound in such a manner that the lead portions 21 on theterminal ends of the wound wire can be located to the side of the flangeportion 12. Such an air core coil 20 is secured to the step portion 12 aon the upper surface of the flange portion 12 of the holder 10 with anadhesive. In this regard, it should be noted that the coil 20 is notlimited to such a air core described above, and it may be

contemplated, for example, to directly wind a coil around thecylindrical portion 11 of the holder 10.

Referring to FIG. 4, the yoke 30 includes an inner cylindrical portion31 of cylindrical shape having an insertion bore 35 into which thecylindrical portion 11 of the holder 10 is inserted, an outercylindrical portion 32 of cylindrical shape provided outside of theinner cylindrical portion 31 with a predetermined spacing lefttherebetween, and a connecting portion 34 for integrally interconnectingthe ends of the inner cylindrical portion 31 and the outer cylindricalportion 32 at opposite side from the flange portion 12 of the holder 10.The yoke 30 is adapted to accommodate the coil 20 within the space ofpredetermined gap size between the inner cylindrical portion 31 and theouter cylindrical portion 32 of the yoke 30.

The yoke 30 is made of a magnetic material, e.g., iron whose surface isplated with nickel. The cylindrical portion 11 of the holder 10 isinserted into the insertion bore 35 of the inner cylindrical portion 31of the yoke 30 displaceably in the optical axis direction. For thispurpose, the insertion bore 35 of the inner cylindrical portion 31 isformed such that it has a diameter greater than the diameter of theouter periphery of the cylindrical portion 11 of the holder 10 butsmaller than the diameter of the peripheral edge of the flange portion12 of the holder 10.

Moreover, as illustrated in FIGS. 2 through 4, the yoke 30 is formed sothat the height in the optical axis direction of the inner cylindricalportion 31 as measured from the connecting portion 34 is smaller thanthe height in the optical axis direction of the outer cylindricalportion 32.

A plurality of, e.g., four, permanent magnets 40 are disposed on themagnet mounting surface 33 of the inner periphery of the outercylindrical portion 32 of the yoke 30 in a spaced-apart confrontingrelationship with the coil 20. It should be noted that the magnetmounting surface 33 is not limited to the one provided, as describedabove, on the inner periphery of the outer cylindrical portion 32 of theyoke 30 but may be provided on the outer periphery of the innercylindrical portion 31, if desired.

Each of the permanent magnets 40 consists of an arcuate permanent magnetextending over a sector of about 90 degrees along the contour of thecircular magnet mounting surface 33. The permanent magnets 40 are madeof neodymium. Each of permanent magnets 40 is magnetized such that, forexample, the curved surface of the respective permanent magnet 40 keptin contact with the magnet mounting surface 33 is a south pole (S-pole)and the opposite curved surface is a north pole (N-pole). The outerperiphery of the inner cylindrical portion 31 of the yoke 30 becomes anS-pole as these arcuate permanent magnets 40 are attached to the yoke 30of cylindrical configuration. This creates a magnetic field that isdirected from the arcuate permanent magnets 40 toward the innercylindrical portion 31. In the event that the coil 20 is supplied withelectric power, a force exerts on the coil 20 in the optical axisdirection by the interaction between the magnetic field of the permanentmagnets and the magnetic field generated by the electric current flowingthrough the coil 22. This makes it possible that the holder 10, that is,the lens assembly 5 is caused to displace in the optical axis direction.In this regard, it should be noted that the number of the permanentmagnets is not particularly limited to four and may be changed to otherplural numbers depending on the circumstances. Further, a singlepermanent magnet of, e.g., C-shape may be employed.

In the meantime, with the yoke 30 set forth above, the magnetic flux isdoomed to be leaked out downwards, as shown by arrows in FIG. 5, betweenthe adjoining permanent magnets 40 at the open side of the cylindricalyoke 30 which is opposite to the connecting portion 34. In order toprevent such a leakage of the magnetic flux, the yoke 30 is providedwith a leakage preventing means to enhance the driving force of theholder 10.

As the leakage inhibitor means, a magnetic member 50 is disposed tointerconnect the permanent magnets 40 in such a condition that themagnetic member 50 is kept in contact with the lower end surfaces of thepermanent magnets 40, that is, the surfaces of the permanent magnets 40that are opposite to the surfaces thereof in contact with the connectingportion 34 of the cylindrical yoke 30. As shown in FIG. 6, the magneticmember 50 functions to reduce the amount of the magnetic flux whichwould otherwise be leaked out downwards. This will increase the magneticflux that is directed from the permanent magnets 40 toward the innercylindrical portion 31 of the cylindrical yoke 30. As depicted in toFIG. 7, according to the actuator 1 described above, the magnetic member50 having an annular ring shape is attracted into contact with thepermanent magnets 40 and then bonded to the permanent magnets 40 with anadhesive. Referring back to FIG. 6, the ring-shaped magnetic member 50has the same width as the radial thickness of the arcuate permanentmagnets 40. This allows the coil 20 to be disposed in the yoke 30 withno hindrance. Furthermore, under the state that the magnetic member 50is attached to the permanent magnets 40, the lower surface of thering-shaped magnetic member 50 is positioned at an upper elevation thanthe end surface of the outer cylindrical portion 32 of the yoke 30. Thispermits the lower leaf spring 60L to be attached to the end surface ofthe outer cylindrical portion 32 of the yoke 30 with no hindrance.Alternatively, the magnetic member 50 may be so sized that the bottomsurface of the magnetic member 50 is flush with the end surface of theouter cylindrical portion 32 of the yoke 30 in the optical axisdirection and such a magnetic member 50 is attached to the lower endsurfaces of the permanent magnets 40, it becomes possible to utilize thebottom surface of the magnetic member 50 as an additional bondingsurface with the lower leaf spring 60L.

In addition, there may a case that the corner portion defined by themagnet mounting surface 33 and the connecting portion 34 of the yoke 30has a different contour than the corresponding corner portion of thepermanent magnets 40. As a result, each of the permanent magnets 40cannot make surface-to-surface contact with the magnet mounting surface33 of the yoke 30, thereby reducing the magnetic efficiency. In such acase, another magnetic member 50 may be also inserted between theconnecting portion 34 of the yoke 30 and the upper end surfaces of thepermanent magnets 40 to thereby assure that the permanent magnets 40 canbe brought into surface-to-surface contact with the magnet mountingsurface 33 of the yoke 30 regardless of the contour of the cornerportion of the yoke 39.

According to the actuator 1 described herein, the magnetic member 50 ismade of a cold-rolled steel plate. However, the material for themagnetic member 50 is not particularly limited to steel but may includeiron, nickel, cobalt and alloy of these metal elements.

Similarly, in the case of employing a single permanent magnet of, e.g.,C-shape, the magnetic member 50 is disposed in contact with the lowerend surfaces of the permanent magnets 40. This can suppress leakage ofthe magnetic flux which would otherwise be leaked out downwards betweenthe opposite circumferential end surfaces of the C-shaped permanentmagnet.

Referring to FIG. 8, the leaf springs, namely, the upper leaf spring 60Uand the lower leaf spring 60L, are made of a sheet-shaped metalmaterial. Each of the upper leaf spring 60U and the lower leaf spring60L is in the form of a gimbal spring that has an inner annulus 61, anouter annulus 62 provided in a spaced-apart relationship with the innerannulus 61, and a plurality of bridge portions 63 joining the innerannulus 61 and the outer annulus 62 together. The bridge portions 63will be elastically deformed if a load is applied to the inner annulus61 under the state that the outer annulus 62 remains fixedly secured.This means that the upper leaf spring 60U and the lower leaf spring 60Lcan support the holder 10, to which the inner annulus 61 is bonded,displaceably in the optical axis direction with the holder 10 beingpositioned in a radial direction thereof (that is, under the conditionthat radial displacement of the holder 10 is being restricted).

Formed on the top surface of the holder 10 is a step portion 16 thatserves to align the upper leaf spring 60U with respect to the holder 10in the process of assembly. This step portion 16 has a cross-sectionalconfiguration that corresponds to the inner circumferential edge of theinner annulus 61. The upper leaf spring 60U is placed onto the topsurface of the holder 10 with the inner annulus 61 thereof coupled tothe step portion 16, and further a stopper 70 is attached onto the upperleaf spring 60U. The inner annulus 61 is bonded to the holder 10 underthe state that it is sandwiched between the top surface of the holder 10and the bottom surface of the stopper 70. Likewise, the outer annulus 62is bonded to the cover 80 and the yoke 30 under the condition that it issandwiched between the bottom surface of the cover 80 and the topsurface of the connecting portion 34 of the yoke 30.

As described above, a step portion 15 for positionally aligning thelower leaf spring 60L in the process of assembly is formed on the bottomsurface of the flange portion 12 of the holder 10. This step portion 15has a cross-sectional configuration that corresponds to the innercircumferential edge of the inner annulus 61. Therefore, the innerannulus 61 is bonded to the holder 10 under the state that it ispositionally aligned with respect to the holder 10. Likewise, the outerannulus 62 is bonded to the base 85 and the yoke 30 under the conditionthat it is sandwiched between the end surface of the outer cylindricalportion 32 of the yoke 30 and the top surface of the base 85.

As illustrated in FIG. 3, a sheet-like electrode 90 is provided betweenthe lower leaf spring 60L and the base 85 to supply electric power tothe coil 20. Referring to FIG. 9, the sheet-like electrode 90 is made ofa polyimide sheet, and has a generally circular ring-like portion 91 andan extension portion 92 extending radially outwardly from the ring-likeportion 91.

A pair of copper-made terminal portions 93 are formed on one surface ofthe sheet-like electrode 90 in such a manner that it can extend from theextension portion 92 to the ring-like portion 91. Provided between thefrontal ends of the two terminal portions 93 on the ring-like portion 91is a dummy terminal portion 95 to which a dummy wire 23 described lateris soldered.

Adhesive layers (not shown) that function to bond the sheet-likeelectrode 90 to the bottom surface of the outer annulus 62 of the lowerleaf spring 60L are formed on the other surface of the sheet-likeelectrode 90 at the positions corresponding to the ring-like portion 91,the joining part of the extension portion 92 with the ring-like portion91 and the frontal end part of the extension portion 92.

The extension portion 92 is adapted to extend to the outside of thesupport frame through an insert hole 88 of the base 85 described laterand then can be connected to a sensor board not shown in the drawings.In order to have the extension portion 92 fitted through the insert hole88, there is a need to bend the extension portion 92 substantially at aright angle with respect to the ring-like portion 91. A polyimide coverfilm 94 is provided over the terminal portions 93 for

the sake of avoiding any damage of the terminal portions 93 which wouldotherwise occur during the bending process.

The two lead portions 21 of the coil 20 are soldered at their front endsto the two terminal portions 93 that are provided on the ring-likeportion 91 of the sheet-like electrode 90, thus permitting the electricpower to be supplied to the coil 20. In the meantime, the lead portions21 may make an unwanted contact with other components as the holder 10is caused to be displaced, and thereby a stress may be concentrated onthe soldered front ends of the lead portions 21. In view of this, asillustrated in FIG. 10, base parts of the lead portions 21 of the wireof the coil 20 are respectively wound around two of the three smallbosses 13 provided on the step portion 15 of the bottom surface of theflange portion 12 of the holder 10. Subsequently, the front ends of thelead portions 21 are soldered to the terminal portions 93 of thesheet-like electrode 90, respectively.

Each of the bosses 13 is of cylindrical shape and has a height smallenough to avoid any contact, in an assembled condition, with the topsurface of a bottom plate portion 86 of the base 85 described later.

Each of the lead portions 21 extends from the coil 20 into the bottomsurface side of the flange portion 12 of the holder 10 through a recess14 (see FIG. 12) formed on the peripheral edge of the flange portion 12.Then, the lead portions 21 are respectively wound around thecorresponding bosses 13 located in the vicinity of the recess 14.

The lead portions 21 running between the bosses 13 and the solderingportions 22 are provided in a loosened condition to avoid any tensilestress which would otherwise be generated in the lead portions 21 as theholder 10 is caused to be displaced.

In the autofocus actuator 1 described above, as illustrated in FIG. 11,a stress relief agent 24 is applied to cover both the winding partswhere the lead portions 21 are wound around the bosses 13 of the holder10 and the soldering parts 22 where the front ends of the lead portions21 are soldered to the terminal portions 93 of the sheet-like electrode90. This helps prevent the stress from concentrating on a local part ofeach lead portion 21.

Referring to FIG. 12, the bosses 13 are three in number and provided onthe bottom surface of the flange portion 12 substantially at an equalspacing. Each of the three bosses 13 is inserted through a semicircularrecess 66 (see FIG. 8) that lies on the inner edge of the inner annulus61 of the lower leaf spring 60L bonded to the bottom surface of theflange portion 12.

As described above, the lead portions 21 of the coil 20 are wound aroundtwo of the three bosses 13. The remaining one boss 13 is used to supporta balance keeping means.

The balance keeping means comprises a dummy wire 23 which is the same asthat used in the coil 20. One end of the dummy wire 23 is wound on thecorresponding boss 13, while the other end thereof is soldered to thedummy terminal portion 95 of the sheet-like electrode 90. This assuresthat the weight of the holder 10 is well balanced, thereby making itpossible to displace the holder 10 in the optical axis direction with astabilized posture.

A stress relief agent 24 is also applied to the dummy wire 23 so as tocover both the winding part wound on the boss 13 and the soldering partof the dummy wire 23. This helps prevent the stress from concentratingon a local part of the dummy wire 23 and assists in balancing the weightof the holder 10.

It should be noted that the actuator 1 is not particularly limited tothe use of the above-mentioned sheet-like electrode 90. For example, ifdesired, a terminal portion for connection with the power source may beformed, by use of an insulating material, on a part of the bottomsurface (the opposite surface from the holder 10) of the outer annulus62 of the lower leaf spring 60L that is not displaced in accordance withthe displacement of the holder 10, and then the front ends of the leadportions 21 of the coil 20 may be connected to the terminal portion soformed.

Referring to FIG. 13, the stopper 70 is made of synthetic resin in theform of a ring and will be subjected to bonding under the state that theinner annulus 61 of the upper leaf spring 60U is sandwiched between theholder 10 and the stopper 70.

The stopper 70 is assembled in such a manner that a part of the edge ofeach of three apertures 71 is in exact alignment with the contour ofeach of the semicircular recesses 65 (see FIG. 8) formed on theperipheral edge of the inner annulus 61 of the upper leaf spring 60U.This makes it possible to ascertain the clearance between thecylindrical portion 11 of the holder 10 and the inner cylindricalportion 31 of the yoke 30 by seeing through the apertures 71 and thesemicircular recesses 65 from the top.

Referring back to FIG. 2, the upper leaf spring 60U is assembled suchthat a part of the outer annulus 62 of the upper leaf spring 60U can besandwiched between the connecting portion 34 of the yoke 30 and thecover 80. The cover 80 is provided with a generally rectangular topplate portion 81 having an opening 80 a and a plurality of post portions82 respectively formed at the corners of the top plate portion 81 insuch a manner that the post portions 82 extend vertically downwardlyfrom the top plate portion 81.

The lower leaf spring 60L is assembled such that a part of the outerannulus 62 of the lower leaf spring 60L can be sandwiched between theend surface of the outer cylindrical portion 32 of the yoke 30 and thebase 85. The base 85 is provided with a generally rectangular bottomplate portion 86 having an opening 85 a and a plurality of post portions87 respectively formed at the corners of the bottom plate portion 86 insuch a manner that the post portions 87 extend vertically upwardly fromthe bottom plate portion 86.

The post portions 82 of the cover 80 and the post portions 87 of thebase 85 correspond in their positions and are insertedly coupled witheach other. This allows the cover 80 and the base 85 to be readilyaligned in the process of assembly and then bonded together.

Turning to FIG. 14, three protrusions 80 b of generally triangular shapeare provided along the inner edge of the opening 80 a of the cover 80.These three protrusions 80 b are so disposed that they can be insertedlycoupled with three recesses 72 of generally triangular configurationformed along the outer edge of the stopper 70, with a gap lefttherebetween. This helps prevent any movement in the circumferentialdirection of the holder 10 that remains bonded to the stopper 70.Accordingly, it becomes possible to have the lens assembly 5 threadedlycoupled to the holder 10 with ease in the process of assembly, withouthaving to cause such problems as plastic deformation of the bridgeportions 63 of the leaf springs 60, peeling-off of the contact surfacesbetween the individual components and severing-apart of the leadportions 21 of the coil 20.

Provided above the outer edge of the stopper 70 are lug portions 83 eachprojecting radially inwardly from the opening 80 a. These lug portions83 are adapted to abut against the stopper 70 to thereby suppress anyunwanted displacement of the holder 10 in such an instance that a greatmagnitude of force exerts on the holder 10 by a dropping shock, etc.This also helps avoid plastic deformation of the bridge portions 63 ofthe leaf springs 60 supporting the holder 10, peeling-off of the contactsurfaces between the individual components and severing-apart of thelead portions 21 of the coil 20.

As shown in FIG. 2, the bottom plate portion 86 of the base 85 has aninsert hole 88 through which the extension portion 92 of the sheet-likeelectrode 90 passes in the process of assembly.

Referring to FIG. 3, three projections 89 are integrally formed on thebottom plate portion 86 of the base 85 in the vicinity of the opening 85a and at a generally equal spacing in the circumferential direction.When assembled, the distal ends of the projections 89 remain in contactwith the bottom surface of the flange portion 12 of the holder 10, forexample. The height of each projection 89 is greater than the distancebetween the top surface of the bottom plate portion 86 of the base 85and the lower leaf spring 60L. This means that the holder 10 is keptdisplaced in the upward direction. As a result, a resilient force isdownwardly exerting on the respective leaf springs 60U and 60L thatsupport the holder 10, thereby normally applying a back tension to theholder 10.

As illustrated in FIG. 2, three circular holes 86 a are formed throughthe bottom plate portion 86 of the base 85 along the circumference ofthe opening 85 a at a generally equal spacing. The condition of thesoldering portion 22 on the sheet-like electrode 90 can be observedthrough the circular holes 86 a from the outside of the base 85.

Hereinbelow, a description will be made with regard to the steps ofassembling the autofocus actuator 1 described above.

(1) The coil 20 is adhesively affixed to the step portion 12 a on thetop surface of the flange portion 12 of the holder 10.

(2) Next, four pieces of the permanent magnets 40 are arranged inpredetermined positions and bonded to the magnet mounting surface 33 onthe inner periphery of the outer cylindrical portion 32 of the yoke 30with an adhesive. Under this state, the magnetic member 50 is attractedinto contact with the bottom end surfaces of the permanent magnets 40and then bonded thereto.

(3) Next, the holder 10 to which the coil 20 has been affixed assembledwith the yoke 30 on which the magnetic member 50 has been mounted in thepreceding step. At this time, the cylindrical portion 11 of the holder10 is inserted into the insertion bore 35 of the inner cylindricalportion 31 of the yoke 30. The holder 10 and the yoke 30 are assembledsuch that the coil 20 can be accommodated within the space between theouter periphery of the inner cylindrical portion 31 of the yoke 30 andthe permanent magnets 40.

(4) Next, under the state of step (3), the inner annuluses 61 of therespective leaf springs 60U and 60L are insertedly coupled with the topand bottom step portions 15, 16 of the holder 10, respectively, and thenbonded thereto with an adhesive.

(5) Next, the stopper 70 is adhesively secured to the top surface of theupper leaf spring 60U already bonded at step (4) in a condition that theinner annulus 61 of the upper leaf spring 60U is sandwiched between thetop surface of the cylindrical portion 11 of the holder 10 and thestopper 70.

(6) Next, the ring-like portion 91 of the sheet-like electrode 90 isbonded, by way of its adhesive layer, to the outer annulus 62 of thelower leaf spring 60L already bonded at step (4).

(7) Next, the lead portions 21 of the coil 20 and the dummy wire 23 arewound around the bosses 13 of the holder 10. Then, the front ends of thelead portion 21 and the dummy wire 23 are soldered to the terminalportions 93 of the sheet-like electrode 90 already bonded at step (6)and the dummy terminal portion 95, after which a stress relief agent 24is applied to the winding parts of the bosses 13 and the soldering parts22.

(8) Next, the cover 80 and the base 85 are attached to the assemblyobtained at step (7) in such a manner that they can sandwich the outerannuluses 62 of the respective leaf springs 60U, 60L between the yoke 30and themselves. The outer annulus 62 of the upper leaf spring 60U, whichlies between the yoke 30 and the cover 80, is then bonded to the yoke 30and the cover 80. Likewise, the outer annulus 62 of the lower leafspring 60L, which lies between the bottom end surface of the outercylindrical portion 32 of the yoke 30 and the base 85, is bonded to thebottom end surface of the outer cylindrical portion 32 of the yoke 30and the base 85. At this moment, the extension portion 92 of thesheet-like electrode 90 is extended to the outside through the inserthole 88 of the base 85.

(9) Next, the lens assembly 5 is threadedly coupled with the threadportion of the holder 10 of the assembly assembled up to step (8).

Hereinbelow, an operation of the autofocus actuator 1 described abovewill now be described.

As viewed in FIG. 3, the magnetic field is caused to direct from thepermanent magnets 40 to the inner cylindrical portion 31 of the yoke 30.If the holder 10 assumes its initial position and electric current flowsin the counterclockwise direction as the coil 20 is viewed from the top,an upwardly exerting electromagnetic force is generated in the coil 20,i.e., the holder 10. This enables the holder 10 to be displaced untilthe electromagnetic force comes into balance with the resilient force ofthe leaf springs 60 that varies depending on the displacement of theholder 10. The electromagnetic force is controlled by the magnitude ofthe electric current flowing through the coil 20, meaning that theholder 10 and hence the lens assembly 5 can be displaced to a desiredposition by controlling the amount of the electric current. With theautofocus actuator 1, the information on the position of the lensassembly 5 can be obtained from the amount of the electric currentflowing through the coil 20, while the information on the image can bedetected by use of a detector element (not shown) located below theautofocus actuator 1. The autofocus position is specifically defined byway of speedily calculating the positional information and the imageinformation in an operation part equipped with a predetermined autofocusalgorithm. The autofocus actuator 1 can perform the autofocusingoperation by controlling the electric current flowing through the coil20 based on the result so calculated.

Hereinbelow, the preferred embodiment of the holder and the stopper usedin the autofocus actuator according to the present invention will bedescribed in detail.

As described above with reference to the prior art autofocus actuatorshown in FIG. 20, if the holder 10 and the yoke 30 make contact witheach other, namely, if the inner peripheral surface of the innercylindrical portion 31 of the yoke 30 and the outer peripheral surfaceof the cylindrical portion 11 of the holder 10 make contact with eachother, there is the problem that it becomes impossible to move the lensassembly 105 with good precision.

Further, if the space between the inner peripheral surface of the innercylindrical portion 31 and the outer peripheral surface of thecylindrical portion 11 is made large so that the inner peripheralsurface of the inner cylindrical portion 31 and the outer peripheralsurface of the cylindrical portion 11 do not make contact with eachother in order to solve the problem described above, this in turn arisesanother problem in that the shock resistance of the autofocus actuator100 is lowered.

For example, in the case where a portable telephone falls from a heightwhere it was being used, the space between inner peripheral surface ofthe inner cylindrical portion 31 and the outer peripheral surface of thecylindrical portion 11 needs to be made about 0.1 mm in order to ensuresufficient shock resistance.

In order to solve the problem mentioned above, in the autofocus actuator1 having the structure described above, the space between thecylindrical portion 11 of the holder 10 and the inner cylindricalportion 31 of the yoke 30 was confirmed using a microscope to lookthrough the openings 71 of the stopper 70 and the rough semicircularrecesses 65 from the upper surface side of the actuator. However, inthis method, there is the problem that it takes time to carry out theconfirmation operation.

In view of these problems, the present inventors devised a holder and astopper which can easily confirm the space between the yoke and theholder. The preferred embodiment of such holder and stopper isrepresented by the holder 10 and the stopper 70 shown in FIGS. 15 to 19.In this regard, it is to be noted that the autofocus actuator of thisembodiment has the same structures as those of the autofocus actuator 1described above excepting the structures shown in FIGS. 15 to 19.

As shown in FIG. 15 to FIG. 17 light transmission portions (lighttransmission means) 17 are formed at prescribed positions of the flangeportion 12 of the holder 10. Further, as shown in FIG. 18, lighttransmission portions (light transmission means) 77 are formed atprescribed positions of the stopper 70. The light transmission portions17, 77 are through holes which pass through the flange portion 12 andthe stopper 70, respectively. By passing light through the lighttransmission portions 17 (77), the space between inner peripheralsurface of the inner cylindrical portion 31 and the outer peripheralsurface of the cylindrical portion 11, and the light transmissionportions 77 (17), it is possible to confirm the space between the yoke30 and the holder 10.

Further, the light transmission portions 17, 77 are holes which passthrough the flange portion 12 and the stopper 70, and these may besealed with a light transmittance material. The light transmittancematerial may be a transparent resin, for example. Further, the lighttransmittance material has a transparency at a level which makes itpossible to see the space between inner peripheral surface of the innercylindrical portion 31 and the outer peripheral surface of thecylindrical portion 11. In this way, it is possible to prevent dust,water and the like from entering into the inside of the autofocusactuator 1 from the light transmission portions 77.

Further, instead of the holes passing through the flange portion 12 andthe stopper 70, the light transmission portions 17, 77 may be formedinto thin film-shaped portions integrally formed with the flange portion12 and the stopper 70, respectively. Preferably, the thin-film shapedportions have a thickness at a level which allows light to passtherethrough. For example, the thin film-shaped portions may have athickness of about 0.1 mm which can ensure light transmittance. Thesethin film-shaped portions are advantageous, since not only they transmitlight but also they make it possible to prevent dust, water and the likefrom entering into the inside of the autofocus actuator 1 from the lighttransmission portions 77. Furthermore, the holder 10 and the stopper 70having such thin film-shaped portions as the light transmission portions17, 77 can be made easily by integral molding without increasing thenumber of steps of the conventional manufacturing process.

Further, as shown in FIG. 17, a protrusion 18 which extends in the axialdirection of the cylindrical portion 11 is formed on the outerperipheral surface of the cylindrical portion 11. As shown in FIG. 19,the protrusions 18 and the inner peripheral surface of the innercylindrical portion 31 are designed to be visible inside the lighttransmission portions 17, 77. In the present embodiment, the innerperipheral surface of the inner cylindrical portion 31, the outerperipheral surface of the cylindrical portion 11 and the protrusions 18are formed to be visible from the light transmission portions 17, 77.Further, each protrusion 18 is constructed from a center convex portion18 a and concave portions 18 b on both sides in the circumferentialdirection of the convex portion 18 a. The tip of the convex portion 18 ais formed to be closer to the inner peripheral surface of the innercylindrical portion 31 than the outer peripheral surface of thecylindrical portion 11. In this way, by seeing light passing near thetip of the protrusion 18, it is possible to confirm the space betweenthe yoke 30 and the holder 10.

As shown in FIGS. 15 to 18, in the present embodiment, a lighttransmission portion 17 and a protrusion 18 are formed at threelocations at 120° spacing in the circumferential direction of the flangeportion 12 and the cylindrical portion 11. In this way, it is possibleto see the space between the inner peripheral surface of the innercylindrical portion 31 and the outer peripheral surface of thecylindrical portion 11 at three positions at the very least, and thismakes it possible to improve the accuracy of confirming contact betweenthe yoke 30 and the holder 10.

Further, the three light transmission portions 17 of the flange portion12 and the three light transmission portions 77 of the stopper 70 areformed at positions which will be opposed to each other in the opticalaxis direction in an assembled state. In this way, it is possible to seethe space between the inner peripheral surface of the inner cylindricalportion 31 and the outer peripheral surface of the cylindrical portion11 in the spaces between the light transmission portions 17 of theflange portion 12 and the light transmission portions 77 of the stopper70, and this makes it possible to improve the accuracy of confirmingcontact between the yoke 30 and the holder 10 further.

Further, as shown in FIGS. 15 to 18, the light transmission portions 17,77 have elliptical shapes in which the major axis bends in thecircumferential direction of the flange portion 12 and the stopper 70along the space between the inner peripheral surface of the innercylindrical portion 31 and the outer peripheral surface of thecylindrical portion 11. In this way, it is possible to efficiently widenthe area in which it is possible to confirm contact between the innerperipheral surface of the inner cylindrical portion 31 and the outerperipheral surface of the cylindrical portion 11 without lowering thestrength of the flange portion 12 and the stopper 70.

With the autofocus actuator 1 according to the preferred embodiments ofthe present invention described above, it is possible to easily checkwhether or not there is contact between the inner cylindrical portion 31of the yoke 30 and the cylindrical portion 11 of the holder 10 byconfirming the passing of light through the light transmission portions17, 77 in the state where the autofocus actuator 1 is assembled. In thisway, it is possible to easily carry out a defective product search evenwhen the space between the inner cylindrical portion 31 of the yoke 30and the cylindrical portion 11 of the holder 10 is designed to be smallin order to improve shock resistance.

Further, in the present embodiment, a description was given for the casein which light transmission portions 17, 77 and protrusions 18 wereformed in at least three places at equal spacing in the circumferentialdirection of the flange portion 12, the stopper 70 and the cylindricalportion 11, but the autofocus actuator of the present invention is notlimited to this, and it is possible to form light transmission portionsand a protrusion at four or more places.

Furthermore, in the present embodiment, a description was given for thecase in which the light transmission portions 17, 77 have ellipticalshapes in which the major axis bends in the circumferential direction ofthe flange portion 12 and the stopper 70, but the autofocus actuator ofthe present invention is not limited to this, and other shapes may beused. For example, it is possible to confirm contact between the outerperipheral surface of the cylindrical portion and the tip of theprotrusion and the inner peripheral surface of an inner cylindricalportion having a rectangular shape or the like.

Moreover, in the present embodiment, a description was given for thecase in which the light transmittance material sealing the lighttransmission portions 77 of the stopper 70 is a transparent resin, butthe autofocus actuator of the present invention is not limited to this,and other transparent materials such as glass or the like may be used,for example.

Finally, it is also to be understood that the present disclosure relatesto subject matter contained in Japanese Patent Application No.2005-067932 (filed on Mar. 10, 2005) which is expressly incorporatedherein by reference in its entirety.

Further, it should also be understood that the present invention is notlimited to the preferred embodiments described hereinabove and, needlessto say, a variety of modifications or variations may be made withoutdeparting from the scope of the invention defined in the followingclaims.

1. An autofocus actuator, comprising: a holder including a cylindricalportion having one end to which a lens unit is attached and a flangeportion provided on the outer periphery of the other end of thecylindrical portion; a coil fixedly secured to the flange portion of theholder in such a manner as to surround the cylindrical portion of theholder; a yoke including an inner cylindrical portion having aninsertion bore into which the cylindrical portion of the holder isinserted, an outer cylindrical portion provided outside the innercylindrical portion with a predetermined spacing left therebetween, anda connecting portion for integrally interconnecting the ends of theinner cylindrical portion and the outer cylindrical portion at oppositeside from the flange portion of the holder, the yoke adapted toaccommodate the coil within the space of a predetermined gap sizebetween the inner cylindrical portion and the outer cylindrical portion;a plurality of permanent magnets disposed on a magnet mounting surfaceof the inner periphery of the outer cylindrical portion of the yoke in aspaced-apart confronting relationship with the coil; a pair of leafsprings including an upper leaf spring and a lower leaf spring providedon opposite end sides in an optical axis direction of the cylindricalportion of the holder, respectively, for supporting the holderdisplaceably in the optical axis direction with the holder beingpositioned in a radial direction thereof; and a stopper attached to theone end of the cylindrical portion of the holder which protrudes fromthe inner cylindrical portion of the yoke for supporting the upper leafspring between the holder and the stopper in a sandwich manner, whereinthe holder in which the lens unit is incorporated being capable ofadjusting its position in the optical axis direction by supplyingelectrical power to the coil; wherein the autofocus actuator furthercomprising light transmission means for confirming the space between theinner peripheral surface of the inner cylindrical portion and the outerperipheral surface of the cylindrical portion of the holder, the lighttransmission means being provided at predetermined positions of theflange portion and the stopper, respectively, so that light can passtherethrough.
 2. The autofocus actuator as claimed in claim 1, whereinthe light transmission means includes through holes formed in the flangeportion and the stopper, respectively, so that light can pass throughthe through holes.
 3. The autofocus actuator as claimed in claim 2,wherein the through holes are sealed with a light transmittancematerial.
 4. The autofocus actuator as claimed in claim 1, wherein eachof the light transmission means is formed into a thin film-shapedportion integrally formed in the flange portion and the stopper.
 5. Theautofocus actuator as claimed in claim 1, wherein on the outer peripheryof the cylindrical portion, at least one protrusion is formed so as toextend in the axial direction of the cylindrical portion, and theprotrusion and the inner surface of the inner cylindrical portion aredisposed so that they can be seen from the light transmission means. 6.The autofocus actuator as claimed in claim 5, wherein the lighttransmission means in the flange portion, the light transmission meansin the stopper and the at least one protrusion are provided at threelocations, respectively, so at to have a predetermined spacing in thecircumferential direction thereof.
 7. The autofocus actuator as claimedin claim 1, wherein the light transmission means in the flange portionand the light transmission means in the stopper are positioned so as tobe opposed to each other in the optical axis direction.
 8. The autofocusactuator as claimed in claim 1, wherein each of the light transmissionmeans is formed into a roughly elliptical shape of which major axisbends in the circumferential direction of the flange portion 12 and thestopper.